Quartz glass crucible for pulling up silicon single crystal and method for manufacture thereof

ABSTRACT

A quartz glass crucible which has a non-transparent outer layer formed through melting a natural silica powder and a transparent layer formed in the inside of the outer layer, wherein the transparent layer comprises a natural quartz layer having a thickness of 0.4 to 5.0 mm transparent layer comprising a synthetic quarts glass is formed thereon in the inside of the crucible in the range of 0.15 to 0.55 L relative to L, which is the distance from the center of the bottom of the inner surface of the quartz glass crucible to the upper end thereof along the inner surface thereof. The quartz glass crucible can be suitably used for suppressing the occurrence of vibration and reducing the generation of roughened face in the surface of a crucible, and thus for pulling up a silicon single crystal with enhanced stability.

TECHNICAL FIELD

The present invention relates to a quartz glass crucible for pulling upa silicon single crystal and a process for producing the same.

JOINT RESEARCH AGREEMENT

The invention of this application was developed under a joint researchagreement between Heraeus Quarzglas & Co. KG and Shin-Etsu QuartzProducts, Ltd., to which a linked agreement was executed between HeraeusQuarzglas GmbH & Co., Shin-Etsu Quartz Products, Ltd., and HeraeusShin-Etsu America, Inc.

BACKGROUND ART

A method which is called Czochralski method (CZ method) has heretoforewidely been adopted in production of silicon single crystals. This CZmethod is a method in which polycrystal silicon is melted in a cruciblemade of a quartz glass, a seed crystal of a silicon single crystal isdipped into this silicon melt and the seed crystal is gradually pulledup while rotating the crucible, to grow a silicon single crystal byemploying a seed crystal as a nucleus. It is necessary that the singlecrystal produced by the above-mentioned CZ method is of high purity andis also enabled to produce a silicon wafer in high yield. As for aquartz glass crucible to be used in the production, a quartz glasscrucible having a two layer structure comprising a transparent innerlayer that does not contain bubbles and an opaque outer, layer thatcontains bubbles is generally used.

In recent years, as a silicon single crystal is made large in diameter,the time for the operation of pulling up of the single crystal becomeslonger and the inner surface thereof contacts a silicon melt at atemperature of 1400° C. or higher for a long time. The inner surfacethereof reacts with the silicon melt and crystallization occurs in ashallow layer of the inner surface, thereby causing the occurrence ofbrown cristobalite in the form of ring (hereinafter referred to as abrown ring). In the above-mentioned brown ring, there is no cristobalitelayer or even if there is, it is a very thin layer, however, as theoperating time elapses, the brown ring expands its size and continues togrow while fusing with each other. Finally, the central portion thereofis eroded to become an uneven glass dissolving surface. Once this glassdissolving surface emerges, dislocations are liable to be generated in asilicon single crystal, which entails inconvenience in the yield in thepulling up of a single crystal. In particular, in order to grow asilicon single crystal for producing a wafer with a large diameter ofnot smaller than 200 mm, it is necessary to perform the operation in theCZ method for more than 100 hours, whereby the emergence of theabove-mentioned glass dissolving surface becomes prominent.

It is considered that the above-mentioned brown ring occurs byemploying, as a nucleus, a minute scratch on the glass surface, aportion of crystalline residue, which is an undissolved residue of a rawmaterial powder, a defect of the glass structure or the like. In orderto reduce the number thereof, the condition of the glass surface ismaintained good, melting is performed at a high temperature for a longtime for reducing a crystalline residual component, or as described inJapanese Patent Nos. 2811290 and 2933404, an amorphous synthetic powderis used as a raw material powder for forming the inner surface thereof.With regard to a synthetic quartz glass made of the above-mentionedamorphous synthetic powder, there are advantages in that the content ofimpurities can be made extremely low and the occurrence of surfaceroughness or brown rings on the inner surface of a crucible inaccordance with the pulling up of a silicon single crystal can bereduced. However, in the case where a transparent inner layer iscomposed of a synthetic quartz glass and an outer layer is composed ofan opaque quartz glass made of natural quartz glass, the physicalproperties vary widely between the transparent inner layer and the outerlayer such as the difference between the fact that one is transparentand the other is opaque and the difference between the fact that one ismade of a synthetic substance and the other is made of a natural one,therefore distortion is generated at the boundary between both layers.In particular, there was a problem of deformation or peel-off of thetransparent inner layer at a bent portion of a crucible to which a highheat load by a heater was applied and which was contacted with a siliconmelt for a long time in some cases. In addition, a crucible comprising atransparent inner layer made of a synthetic quartz glass had a drawbackin that when a polysilicon was melted, the surface of the melt wasliable to vibrate compared with a crucible comprising a transparentinner layer made of natural quartz glass. This vibration was frequentlyobserved particularly at the time from seeding to shoulder formation andin the step of pulling up a front half portion of a single crystal bodyat an initial stage; therefore, it took a long time to perform seeding,a crystal was disordered and melted again, that is, so-called melt backoccurred, and soon, whereby the productivity was decreased in somecases. Therefore, as disclosed in JP-A-2001-348294, a crucible with amultilayer structure having an opaque intermediate layer made of asynthetic quartz glass between a transparent inner layer made of asynthetic quartz glass and an opaque bulk layer made of natural quartzglass has been proposed, however, there was a drawback in that since alarge amount of expensive synthetic quartz powder was used for thecrucible with a multilayer structure, the price of the quartz glasscrucible was high.

The present inventors have continued intensive studies in order toovercome the above-mentioned drawbacks, and as a result, they found thatthe yield in the pulling up of a single crystal is deeply related to theinner surface of the bent portion of a quartz glass crucible andvibration occurring on the surface of a silicon melt is deeply relatedto the inner surface of the straight body portion thereof, and a highyield in the pulling up of a silicon single crystal can be achieved byforming the inner surface at least at the vicinity of the bent portionin a quartz glass crucible to be used for pulling up a silicon singlecrystal with a transparent layer made of a synthetic quartz glass, inaddition, a problem such as deformation or peel-off of the inner layercan be solved by interposing a transparent layer made of natural quartzglass between a transparent layer made of a synthetic quartz glass andan opaque outer layer made of natural quartz glass, further, theoccurrence of vibration on the surface of a silicon melt can besuppressed by forming the inner surface of the straight body portionwith natural quartz glass or with a very thin synthetic quartz glasslayer.

On the other hand, when the number of brown rings occurring on the innersurface of a crucible in the CZ method is reduced, the surface of asilicon melt is liable to vibrate at the time of pulling up a crystal;therefore there is a problem of deterioration of workability. As asolution thereof, it was fount that when the ratio of the number ofbrown rings occurring in the range from the initial surface level of asilicon melt in the pulling up of a single crystal to 0.3 M in terms ofa length M from the initial surface level of the silicon melt to thesurface level of the remaining melt after pulling up a single crystalmeasured along the inner surface of a quartz glass crucible to thenumber of brown rings occurring in the range up to 0.3 M from thesurface level of the remaining melt after pulling up is set in aspecific range or higher, vibration on the surface of the melt does notoccur and the yield in the pulling up of a single crystal becomes high.

Accordingly, an object of the present invention is to provide a quartzglass crucible for pulling up a silicon single crystal in which theoccurrence of vibration on the surface of a melt is suppressed, theoccurrence rate of surface roughness on the inner surface of a crucibleis low even in a long time operation, and a silicon silicon singlecrystal can be stably pulled up.

In addition, an object of the present invention is to provide a methodthat can produce a quartz glass crucible for pulling up a silicon singlecrystal having the above-mentioned excellent properties at low cost.

DISCLOSURE OF THE INVENTION

The present invention firstly relates to a quartz glass crucible forpulling up a silicon single crystal, which has an opaque outer layerformed by melting natural silica powder and a transparent layer formedon the inside thereof, in which the transparent layer is a layer with athickness of 0.4 to 5.0 mm made of natural quartz glass, and atransparent layer made of a synthetic quartz glass is formed on theinside of the crucible in the range from at least 0.15 to 0.55 L interms of a distance L from the center of the bottom of the inner surfaceof the quartz glass crucible to the upper end face along the innersurface of the crucible.

The present invention secondly relates to a quartz glass crucible forpulling up a silicon single crystal, which has an opaque outer layermade of natural quartz glass and a transparent layer formed on theinside thereof, in which the number of brown rings per unit area (cm²)observed in the range from the initial surface level of a silicon meltto 0.3 M in terms of a length M from the initial surface level of thesilicon melt to the surface level of the remaining melt after pulling upa single crystal measured along the inner surface of the quartz glasscrucible is 1.8-fold or more greater than 15 brown rings observed in therange up to 0.3 M above the surface level of the remaining melt.

The present invention thirdly relates to a method for producing theabove-mentioned quartz glass crucible for pulling up a silicon singlecrystal.

The first quartz glass crucible of the present invention is, asdescribed above, a quartz glass crucible in which a transparent Layermade of natural quartz glass is provided on the inside of an opaqueouter layer made of natural quartz glass, a transparent layer made of asynthetic quartz glass is formed on the inside of the crucible in therange from at least 0.15 to 0.55 L in terms of a distance (L) from thecenter of the bottom of the transparent layer to the upper end facealong the inner surface of the crucible, distortion at the boundarybetween the transparent layer made of a synthetic quartz glass and theopaque outer layer made of natural quartz glass is alleviated, anddeformation or peel-off of the transparent layer does not occur. Thethickness of the above-mentioned transparent layer made of naturalquartz glass may be in the range from 0.4 to 5.0 mm, preferably from 0.7to 4.0 mm. When the thickness of the transparent layer made of naturalquartz glass is in the above-mentioned range, the function as abuffering portion is optimized. In addition, the transparent layer madeof a synthetic quartz glass is not formed in the range from 0.6 to 1.0 Lin terms of a distance (L) from the center of the bottom of the innersurface of the crucible to the upper end face along the inner surface ofthe crucible, or even if it is formed, the thickness thereof is set to0.2 mm or less. By forming a transparent layer made of natural quartzglass, not of a synthetic quartz glass, on the inner surface in theabove-mentioned range, vibration of a silicon melt can be suppressed.Further, even if a transparent layer made of a synthetic quartz glass isformed, if the thickness thereof is 0.2 mm or less, the transparentlayer made of a synthetic quartz glass is melted and damaged by the timeof melting a polysilicon (meltdown) and starting the pulling up, and thenatural quartz glass layer is exposed, whereby vibration of a siliconmelt can be suppressed. In this case, compared with a case where atransparent layer made of a synthetic quartz glass is not formed, theamount of natural quartz glass melted in a silicon melt during the meltdown is small, therefore, impurities melted in the silicon melt can bereduced.

Incidentally, the yield in the pulling up of a silicon single crystalvaries depending on dislocation generation in a single crystal, however,it is mostly generated in the latter half of the pulling up step, namelyit is caused by surface roughness on the inner surface or peel-off ofthe inner layer which occurs in the range from the bent portion to thevicinity of the bottom of a quartz glass crucible (in the range from atleast 0.15 to 0.55 L in terms of a distance L from the center of thebottom of the inner surface of the crucible to the upper end face alongthe inner surface thereof) which is contacted with a silicon melt for along time and to which a high heat load by a heater is applied.Therefore, by forming the inner surface in the above-mentioned rangewith a transparent layer made of a synthetic quartz glass, surfaceroughness or peel-off of the inner layer can be significantly reduced.Further, the used amount of a synthetic quartz powder can be reduced,and the cost for producing a quartz glass crucible can be reduced. Thethickness of the above-mentioned transparent layer made of a syntheticquartz glass may be in the range from 0.2 to 1.5 mm. If the thickness isless than 0.2 mm, the effect on suppressing surface roughness orpeel-off of the inner layer is small, and even if a layer with athickness of more than 1.5 mm is formed, the effect on suppressingsurface roughness or peel-off of the inner surface does not change, butthe cost for producing a quartz glass crucible is increased instead,therefore it is not preferred.

In the above-mentioned first quartz glass crucible of the presentinvention, it is preferred that the OH group concentration in the opaqueouter layer made of natural quartz glass is set to low in order toprevent deformation at the time of use at a high temperature. The OHgroup concentration in this opaque outer layer may be set from 20 to 60ppm in terms of an average OH group concentration C_(C). On the otherhand, the OH group concentration in the transparent layer made of asynthetic quartz glass may be set to high, namely from 100 to 300 ppm interms of an average OH group concentration C_(A) in order to improvewettability with a silicon melt. However, in the case where the OH groupconcentration in the inner layer is higher compared with the opaqueouter layer, rapid infrared ray absorption occurs at the boundary wherethe outer layer meets the inner layer, and a load is applied to theboundary, whereby the occurrence frequency of such as deformation orpeel-off is further increased. Accordingly, in this quartz glasscrucible of the present invention, the OH group concentration in thetransparent inner layer made of natural quartz glass provided betweenthe outer layer and the transparent layer is set from 60 to 150 ppm interms of an average OH group concentration C_(B), which is a mean valueof those for the above-mentioned outer layer and transparent layer, andthey are made to satisfy the relation: C_(A)>C_(B)>C_(C), whereby theoccurrence frequency of deformation or peel-off of the inner layer canbe reduced. For adjusting the average OH group concentration C_(A) inthe above-mentioned transparent layer to a high concentration of 200 mmor higher, a method for introducing water vapor in the inside of thecrucible as described in JP-A-2001-348240 or the like may be adopted.

The second quartz glass crucible of the present invention is, asdescribed above, a quartz glass crucible for pulling up a silicon singlecrystal, which has an opaque outer layer made of natural quartz glassand a transparent layer formed on the inside thereof, in which thenumber of brown rings per unit area (cm²) observed in the range from theinitial surface level of a silicon melt to 0.3 M in terms of a length Mfrom the initial surface level of the silicon melt to the surface levelof the remaining melt after pulling up a single crystal measured alongthe inner surface of the quartz glass crucible is 1.8-fold or more,preferably 2.5-fold or more greater than the number of brown ringsobserved in the range up to 0.3 M above the surface level of theremaining melt. The above-mentioned brown ring is a cristobalite brownring as described above, and in the initial stage of the occurrencethereof, as shown in FIG. 4( a), there is no cristobalite layer or evenif there is, it is a very thin layer. As the operating time of pullingup a single crystal elapses, that is, as the time of contacting acrucible with a silicon melt is increased, the brown ring expands itssize and a crystalline texture emerges as shown in FIG. 4( b). Pullingup of a single crystal is further continued, and when the reactionbetween the silicon melt and the crucible proceeds, the portionencircled by the brown ring as shown in FIG. 4( c) is gradually erodedto become a rough glass dissolving surface (amorphous). In FIG. 4, 17indicates the inner surface of a crucible, 18 indicates a brown ring, 19indicates a crystalline texture, and 20 indicates a glass dissolvingsurface. Once this glass dissolving surface emerges, dislocations areliable to be generated in a silicon single crystal, and the rate ofsingle crystallization is decreased.

The above-mentioned number of brown rings is the number per unit area(cm²) calculated by dividing the counted number of brown rings observedin arbitrary three locations with a width of 10 cm in thecircumferential direction of the crucible by the measured area. In thevicinity of the remaining melt which is contacted with the silicon meltin the crucible for a long time and on which a brown ring is liable togrow, brown rings are fused to each other in some cases. In this case,however, the area per one brown ring is calculated from the average sizeof a single brown ring observed in the measured range, the valueobtained by dividing the area of the fused portion by the area per onebrown ring is defined as the number of brown rings in the fused portion.

In the quartz glass crucible to be used in the CZ method, vibration onthe surface of a silicon melt in the CZ method occurs particularlyfrequently in the range where the surface level of the melt is from theinitial surface level of the melt to 0.3 M, however, by increasing thenumber of brown rings only in the range, the above-mentioned vibrationoccurring on the surface of a silicon melt can be suppressed. Inaddition, since the above-mentioned range is contacted with the siliconmelt for a short time, a brown ring is small in size and in a state asshown in FIG. 4 a, and a glass dissolving surface does not occur,therefore, even if the number of brown rings is increased, there is noeffect on the yield in the pulling up of a single crystal.

On the other hand, dislocations in a silicon single crystal are mostlygenerated in the range up to 0.3 M above the surface level of theremaining melt, however, this range is contacted with the silicon meltfor a long time, therefore, a brown ring grows there and a glassdissolving surface as shown in FIG. 4( c) is liable to occur.Accordingly, by decreasing the number of brown rings in this range, theoccurrence of the glass dissolving surface can be suppressed, and theyield in the pulling up of a single crystal can be improved. Inaddition, even if the number of brown rings in this range is decreased,there is no effect on vibration of the silicon melt.

In the CZ method, the number of brown rings may slightly vary dependingon the conditions of pulling up a single crystal even if the samecrucible is used, however, the number of brown rings per unit area (cm²)observed in the range from the initial surface level of a silicon meltto 0.3 M in terms of a length M from the initial surface level of thesilicon melt to the surface level of the remaining melt after pulling upa single crystal measured along the inner surface of the crucible is setto 1.8-fold or more, preferably 2.5-fold or more greater than the numberof brown rings observed in the range up to 0.3 M above the surface levelof the remaining melt. By doing so, vibration occurring on the surfaceof the silicon melt can be suppressed, and the yield in the pulling upof a silicon single crystal can be increased. In particular, the numberof brown rings observed in the range from the initial surface level ofthe melt to 0.3 M is from 2.0 to 5.0/cm², vibration occurring on thesurface of the silicon melt can be surely suppressed. In addition, thenumber of brown rings observed in the range up to 0.3 M above thesurface level of the remaining melt is from 0.02 to 0.9/cm² or less, theyield of silicon single crystal becomes a high level. Further, in thecase where dislocations are generated in a single crystal due to atrouble in the latter half of the step of pulling up a silicon singlecrystal, the crystal is melted again and pulled up again, that is,so-called melt back is carried out in come cases, however, when thismelt back is carried out or multiple pulling up in which several singlecrystals are pulled up from one crucible is carried out, the number ofbrown rings is increased, fusion of brown rings proceeds, andcalculation of the number becomes difficult. In the case where pullingup is carried out without carrying out melt back, or in a state afterthe first pulling up for multiple pulling up is carried out, if acrucible in which the number of brown rings is in the above-mentionedrange is used, favorable pulling up can be achieved compared with acrucible in which the number of brown rings is outside of theabove-mentioned range even when melt back is carried out or multiplepulling up is carried out. Therefore, the calculation of the numbershall be carried out for the inner surface of a crucible after onesingle crystal is pulled up without carrying out melt back.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a first quartz glass crucible ofthe present invention. FIG. 2 is a schematic sectional view of a secondquartz glass crucible of the present invention. FIG. 3 is a schematicview of an apparatus for producing the above-mentioned quartz glasscrucible. FIG. 4 is a partial plan view of an inner surface of a quartzglass crucible showing the occurrence of brown rings which are generatedin the CZ method.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be explained with reference to theaccompanying drawings for describing in more detail.

In FIGS. 1 and 2, 1 indicates a quartz glass crucible, 2 indicates abottom of the crucible, 3 indicates a straight body portion, 4 indicatesan opaque outer layer made of a synthetic quartz glass, 5 indicates atransparent layer made of natural quartz glass, 6 indicates atransparent layer made of a synthetic quartz glass and 7 indicates abent portion. The first quartz glass crucible of the present inventionis, as shown in FIG. 1, a quartz glass crucible having an opaque outerlayer formed by melting natural silica powder and a transparent layerwith a thickness of 0.4 to 5.0 mm made of natural quartz glass formed onthe inside thereof, in which a transparent layer made of a syntheticquartz glass is formed on the inside of the crucible in the range fromat least 0.15 to 0.55 L in terms of a distance L from the center of thebottom of the inner surface of the quartz glass crucible to the upperend face along the inner surface of the crucible. In addition, thesecond quartz glass crucible of the present invention is, as shown inFIG. 2, a quartz glass crucible having an opaque layer made of naturalquartz glass and a transparent layer made of quartz glass formed on theinside thereof, in which the inner surface of the crucible in the rangefrom the initial surface level of the melt to 0.3 M is formed with atransparent layer made of natural quartz glass or a mixture of naturaland synthetic quartz glasses, the inner surface of the crucible in therange up to 0.3 M above the surface level of the remaining melt isformed with a transparent layer made of a synthetic quartz glass, andthe inner surface of the crucible in the range other than above isformed with a transparent layer made of any of natural quartz glass, amixture of natural and synthetic quartz glasses and a synthetic quartzglass. The above-mentioned first and second quartz glass crucibles areproduced by using an apparatus shown in FIG. 3. More specifically, it isa method in which natural silica powder is fed into a rotatable mold 8,and molded in the form of a crucible, then, an arc electrode 14 isinserted in the article, and the opening portion of the crucible-likemolded article is covered with a plate-like lid 11, then, an innercavity of the crucible-like molded article is made a high temperaturegas atmosphere 16 by the arc electrode 14 and at least a portion of theinner cavity is melted and vitrified to form an opaque crucible basebody, subsequently, a synthetic silica powder is fed to the hightemperature atmosphere 16 from a silica powder feeding device 15, andmelted and vitrified to form a transparent layer 6 made of a syntheticquartz glass on the inner surface of the crucible; or, after or duringthe formation of the opaque crucible base body, natural silica powder ofhigh purity or a mixture of natural and synthetic silicas is fed to thehigh temperature atmosphere 16 from a silica powder feeding device 10while regulating the feed rate with a feed rate regulating valve 12, andmelted and vitrified to form a transparent layer 5 made of naturalquartz glass or a mixture of natural and synthetic quartz glasses in therange at least from the initial surface level of the melt to 0.3 M, andfurther a synthetic silica powder is fed to the high temperatureatmosphere 16 from the silica powder feeding device 15, and melted andvitrified to form a transparent layer 6 made of a synthetic quartz glassin the range at least up to 0.3 M above the surface level of theremaining melt excluding the range from the initial surface level of themelt to 0.3 M of the inner surface of the crucible. In particular, withregard to the method for producing the second quartz glass crucible, itcan also be produced by a method in which the entire inner layer of thecrucible is composed of a synthetic quartz glass, the inner surface ofthe crucible in the range from the initial surface level of the melt to0.3 M is subjected to an etching treatment or a sandblast process tomake minute scratches, and the number of brown rings is increased toadjust the ratio of the number of brown rings in the range from theinitial surface level of the melt to 0.3 M to the number of brown ringsin the range up to 0.3 M above the surface level of the remaining meltto 1.8-fold or more, preferably 2.5-fold or more.

EXAMPLES

Hereunder, the present invention will be explained more specificallywith reference to Examples, however, the present invention is notlimited to these.

Example 1

By using an apparatus shown in FIG. 3, natural silica powder of highpurity subjected to a purification treatment was fed into a rotatablemold 8, and a crucible-like molded article 9 was formed by utilizingcentrifugal force. Then, an arc electrode 14 was inserted in thearticle, and the opening portion was covered with a plate-like lid 11.Then, the inside of the inner cavity was made a high temperature gasatmosphere by the arc electrode 14, melted and vitrified, and thencooled, whereby an opaque outer layer 4 with a thickness of 8 to 10 mmwas produced. Subsequently, the inner cavity of the opaque outer layer 4was made a high temperature atmosphere 16 by the arc electrode 14 whilerotating the mold 8, and then natural silica powder was fed at 100 g/minfrom a silica powder feeding nozzle 15, whereby a transparent layer 5with a thickness of 0.9 to 2 mm made of natural quartz glass was fusedand integrated to the inner surface of the opaque outer layer 4.Subsequently, a synthetic silica powder was fed at 100 g/min from thesilica powder feeding nozzle 15, whereby a transparent layer 6 made of asynthetic quartz glass was fused and integrated to the above-mentionedtransparent layer at a thickness of 0.5 to 1.2 mm, at a thickness of 0.2to 0.5 mm, and at a thickness of 0.1 to 0.2 mm in the range up to 0.55L, in the range from 0.55 to 0.6 L and in the range from 0.6 to 1.0 L,respectively in terms of a distance (L) from the center of the bottom ofthe transparent layer to the upper end face along the inner surface ofthe crucible. The diameter of the obtained quartz glass crucible was 24inches, and the average OH group concentration C_(C) in the opaque outerlayer 4 made of natural quartz glass was 40 ppm, the average OH groupconcentration C_(B) in the transparent layer 5 made of natural quartzglass was 110 ppm and the average OH group concentration C_(A) in thetransparent layer 6 made of a synthetic quartz glass was 220 ppm. When apolycrystal silicon was fed into this quartz glass crucible and melted,and pulling up of a single crystal was carried out at N=5 by the CZmethod, vibration of the silicon melt was not observed in any case, andfurther, the average of rate of single crystallization of the obtainedsilicon single crystal was 92%, which showed a high yield.

Examples 2 to 5

In Example 1, the transparent layer 5 made of natural quartz glass andthe transparent layer 6 made of a synthetic quartz glass, which form theinner surface of a quartz glass crucible, were fused and integrated soas to have a thickness shown in Table 1, respectively, whereby a 24-inchquartz glass crucible was produced. The average OH group concentrationin each layer of the produced quartz glass crucible was as shown inTable 1. By using this quartz glass crucible, pulling up of a siliconsingle crystal was carried out in the same manner as in Example 1. Theresults are shown in Table 1.

TABLE 1 Example 2 Example 3 Example 4 Example 5 Transparent layerThickness 0 to 0.55 L: 1 to 3 mm; 0 to 0.1 L: 0 mm; 0 to 0.55 L: 0.3 to0.8 mm; 0 to 0.55 L: made of synthetic 0.55 to 0.6 L: 0.2 to 1 mm; 0.1to 0.15 L: 0 to 0.3 mm: 0.55 to 0.6 L: 0 to 0.3 mm; 0.3 to 0.8 mm;quartz glass 0.6 to 1 L: 0.1 to 0.2 mm 0.15 to 0.55 L: 0.3 to 1.2 mm;0.6 to 1 L: 0 mm 0.55 to 0.6 L: 0.55 to 0.6 L: 0.2 to 0.4 mm; 0 to 0.03mm; 0.6 to 1 L: 0.1 to 0.2 mm 0.6 to 1 L: 0 mm OH group 220 ppm 220 ppm150 ppm 150 ppm Transparent inner Thickness 0.7 to 1 mm 0.9 to 2 mm 1 to3 mm 1 to 3 mm layer made of OH group 110 ppm 110 ppm 80 ppm 80 ppmnatural quartz glass Opaque outer layer Thickness 8 to 10 mm 8 to 10 mm8 to 10 mm 8 to 10 mm made of natural OH group 40 ppm 40 ppm 40 ppm 100ppm quartz glass Number of pulling up operations 5 5 5 5 Production costof crucible Δ ∘∘ ∘∘ ∘∘ Vibration occurring on melt ∘ ∘∘ ∘∘ ∘∘ surfaceAverage rate of single 93% 91% 92% 90% crystallization Remarks There isno problem with A transparent layer There is no problem. There was noproblem the performance, made of synthetic quartz with the performance,however, cost is higher glass is not present at however, the shape iscompared with Example 1. the bottom, however the slightly deformed andyield is favorable. there is some concern.

Comparative Examples 1 to 3

In Example 1, the transparent layer 5 made of natural quartz glass andthe transparent layer 6 made of a synthetic quartz glass, which form theinner surface of a quartz glass crucible, were fused and integrated soas to have a thickness shown in Table 2, respectively, whereby a 24-inchquartz glass crucible was produced. The average OH group concentrationin each layer of the produced quartz glass crucible was as shown inTable 2. By using this quartz glass crucible, pulling up of a siliconsingle crystal was carried out in the same manner as in Example 1. Theresults are shown in Table 2.

TABLE 2 Comparative Example 1 Comparative Example 2 Comparative Example3 Transparent layer made of Thickness None 1 to 3 mm 0 to 0.55 L: 0.9 to0.3 mm; synthetic quartz glass 0.55 to 0.6 L: 0.2 to 0.9 mm; 0.6 to 1 L:0.1 to 0.2 mm OH group — 220 ppm 220 ppm Transparent inner layer madeThickness 1 to 3 mm None None of natural quartz glass OH group 110 ppm —— Opaque outer layer made of Thickness 8 to 10 mm 8 to 10 mm 8 to 10 mmnatural quartz glass OH group 40 ppm 40 ppm 40 ppm Number of pulling upoperations 5 5 5 Production cost of crucible ∘∘ x Δ Vibration occurringon melt surface ∘∘ x ∘ Average rate of single crystallization 30% 75%45% Remarks Disorder frequently occurred Remelting was frequently Therewas a lot in which the in the middle of crystalline performed due tovibration of pulling up operation was body. Surface roughness in themelt surface. A crack halted due to the exposure of the crucible wassignificant. occurred between the the opaque layer in the transparentlayer and the straight body portion. A opaque layer made of naturalcrack similar to that of quartz glass in the bent Comparative Example 2portion. occurred in the bent portion.

Example 6

By using an apparatus shown in FIG. 3, natural silica powder of highpurity subjected to a purification treatment was fed into a rotatablemold 8, and a quartz glass crucible-like molded article 9 was formed byutilizing centrifugal force. Then, an arc electrode 14 was inserted inthe article, and the opening portion was covered with a plate-like lid11. Then, the inside of the inner cavity was made a high temperature gasatmosphere by the arc electrode 14, melted and vitrified, whereby anopaque quartz glass outer layer 4 was produced. Subsequently, naturalsilica powder was fed at 100 g/min from a silica powder feeding device10, whereby a transparent layer 5 made of natural quartz glass was fusedand integrated to the inner surface of the opaque quartz glass outerlayer 4. Then, a synthetic silica powder was fed at 100 g/min from asilica powder feeding device 15, and after the use in the pulling up ofa silicon single crystal, a transparent layer 6 made of a syntheticquartz glass was fused and integrated to the inside of the crucible inthe range from 0.5 to 1.0 M from the initial surface level of a siliconmelt in terms of a length M from the initial surface level of thesilicon melt to the surface level of the remaining melt after pulling upa single crystal measured along the inner surface of the quartz glasscrucible, whereby a quartz glass crucible with an outer diameter of 22inches was produced. By using this quartz glass crucible, pulling up ofa silicon single crystal was carried out by the CZ method. The resultsof the pulling up of a silicon single crystal and the results ofmeasuring the number of brown rings on the inner surface of the crucibleare shown in Table 3.

Example 7

By using an apparatus shown in FIG. 3, natural silica powder of highpurity subjected to a purification treatment was fed into a rotatablemold 8, and a crucible-like molded article 8 was formed by utilizingcentrifugal force. Then, an arc electrode 14 was inserted in thearticle, and the opening portion was covered with a plate-like lid 11.Then, the inside of the inner cavity was made a high temperature gasatmosphere by the arc electrode 14, melted and vitrified, whereby anopaque outer layer 4 was formed. Then, a synthetic silica powder was fedat 100 g/min from a silica powder feeding device 15, whereby atransparent layer made of a synthetic quartz glass was fused andintegrated to the entire inner surface of the opaque outer layer 4.Subsequently, natural silica powder was fed at 100 g/min from a silicapowder feeding device 10, and after the use in the pulling up of asilicon single crystal, a transparent layer made of natural quartz glasswas fused and integrated to the inside of the crucible in the range fromthe initial surface level of a silicon melt to 0.4 M in terms of alength M from the initial surface level of the silicon melt to thesurface level of the remaining melt after pulling up a single crystalmeasured along the inner surface of the quartz glass crucible, whereby aquartz glass crucible with an outer diameter of 22 inches was produced.By using this quartz glass crucible, pulling up of a silicon singlecrystal was carried out by the CZ method. The results of the pulling upof a silicon single crystal and the results of measuring the number ofbrown rings on the inner surface of the crucible are shown in Table 3.

Example 8

By using an apparatus shown in FIG. 3, natural silica powder of highpurity subjected to a purification treatment was fed into a rotatablemold 8, and a crucible-like molded article 9 was formed by utilizingcentrifugal force. Then, an arc electrode 14 was inserted in thearticle, and the opening portion was covered with a plate-like lid 11.Then, the inside of the inner cavity was made a high temperature gasatmosphere by the arc electrode 14, melted and vitrified, whereby anopaque outer layer 4 was formed. Then, a synthetic silica powder was fedat 100 g/min from a silica powder feeding device 15, and a transparentlayer made of a synthetic quartz glass was fused and integrated to theentire inner surface of the opaque outer layer 4, whereby a quartz glasscrucible with an outer diameter of 22 inches was produced. Further, theregion which is the upper straight body portion 3 of the above-mentionedcrucible and in the range from the initial surface level of the siliconmelt to 0.35 M was subjected to an etching treatment with 50% HF for 30minutes as well as a standard HF washing. By using this quartz glasscrucible, pulling up of a silicon single crystal was carried out by theCZ method. The results of the pulling up of a silicon single crystal andthe results of measuring the number of brown rings on the inner surfaceof the crucible are shown in Table 3.

Comparative Example 4

By using an apparatus shown in FIG. 3, natural silica powder of highpurity subjected to a purification treatment was fed into a rotatablemold 8, and a crucible-like molded article 9 was formed by utilizingcentrifugal force. Then, an arc electrode 14 was inserted in thearticle, and the opening portion was covered with a plate-like lid 11.Then, the inside of the inner cavity was made a high temperature gasatmosphere by the arc electrode 14, melted and vitrified, whereby anopaque outer layer 4 was formed. Then, a synthetic silica powder was fedat 100 g/min from a silica powder feeding device 15, and a transparentlayer made of a synthetic quartz glass was fused and integrated to theentire inner surface of the opaque outer layer 4, whereby a quartz glasscrucible with an outer diameter of 22 inches was produced. By using thisquartz glass crucible, pulling up of a silicon single crystal wascarried out by the CZ method. The results of the pulling up of a siliconsingle crystal and the results of measuring the number of brown rings onthe inner surface of the crucible are shown in Table 3.

Comparative Example 5

By using an apparatus shown in FIG. 3, natural silica powder of highpurity subjected to a purification treatment was fed into a rotatablemold 8, and a crucible-like molded article 9 was formed by utilizingcentrifugal force. Then, an arc electrode 14 was inserted in thearticle, and the opening portion was covered with a plate-like lid 11.Then, the inside of the inner cavity was made a high temperature gasatmosphere by the arc electrode 14, melted and vitrified, whereby anopaque outer layer was formed. Then, natural silica powder was fed at100 g/min from a silica powder feeding device 10, and a transparentlayer made of natural quartz glass was fused and integrated to theentire inner surface of the opaque outer layer 4, whereby a quartz glasscrucible with an outer diameter of 22 inches was produced. By using thisquartz glass crucible, pulling up of a silicon single crystal wascarried out by the CZ method. The results of the pulling up of a siliconsingle crystal and the results of measuring the number of brown rings onthe inner surface of the crucible are shown in Table 3.

TABLE 3 Number of brown rings B Number of brown rings A in the in therange up to 0.3 M Average rate of range from the initial surface abovethe surface level of Number Vibration of melt single crystallizationlevel of the melt to 0.3 M the remaining melt A/B Example 6 5 None 93%2.22 0.62 3.6 Example 7 5 None 89% 2.03 0.91 2.2 Example 8 5 There issmall 92% 1.64 0.64 2.6 vibration, however, there is no operationalproblem Comparative 5 Loss of time is 79% 0.52 0.66 0.8 Example 4 greatdue to vibration. Comparative 5 None 48% 2.33 2.42 1.0 Example 5

As is clear from the results shown in Table 3, in the second quartzglass crucible of the present invention, vibration of a silicon melt didnot occur, even if it occurred, it occurred at a level without causingany operational problem, and the rate of single crystallization wasgood. On the contrary, in the conventional quartz glass crucible asshown in Comparative Example 4, since disorder frequently occurred atthe time of seeding or shoulder formation due to vibration of a siliconmelt, Loss of time was great due to melt back and the operating time waslonger. As a result, in the above-mentioned conventional quartz glasscrucible, though the number of brown rings was small, they became largein size, and the occurrence frequency of glass dissolving surface wasincreased, therefore the rate of single crystallization became low.Further, in the crucible having a transparent layer made of naturalquartz glass as shown in Comparative Example 5, vibration of a siliconmelt did not occur, however, the number of brown rings in the vicinityof the remaining melt was large, glass dissolving surface occurred at aconsiderably high frequency, and the rate of single crystallization wasextremely low.

INDUSTRIAL APPLICABILITY

As described above, the quartz glass crucible of the present inventionis useful as a quartz glass crucible for pulling up a silicon singlecrystal because vibration does not occur on the surface of a siliconmelt, surface roughness or peel-off of the inner layer does not occur,and even if it is used for a long time, surface roughness of the innersurface or peel-off of the inner layer does not occur, and pulling up ofa silicon single crystal can be stably carried out for a long time.

1. A quartz glass crucible for pulling up a silicon single crystal,comprising: a quartz glass crucible body having a hollow cylindrical topportion forming an opening into the quartz glass crucible, a bottomportion forming a circular depression with a centrally-located bottomdead center point and a bent portion interconnecting the top portion andthe bottom portion to form an inside surface of the quartz glasscrucible body, the quartz glass crucible body having an opaque outerlayer formed by melting natural silica powder and a transparent layerstructure formed on the inside thereof, characterized in that thetransparent layer structure includes a transparent layer made of naturalquartz glass with a thickness of 0.4 to 5.0 mm covering the entirety ofthe inside of the opaque outer layer, and a transparent layer made of asynthetic quartz glass having a lower transparent layer portion and anupper transparent layer portion, the lower transparent layer portionformed on and covering a lower portion of the transparent layer made ofthe natural quartz glass of the inside of the crucible and having: athickness extending in a range from 0.15 to 0.55 L selected from athickness range of 0.2 to 1.5 mm, the upper transparent layer portionhaving a thickness of 0.1 mm or less and formed on and covering an upperportion of the transparent layer made of the natural quartz glass of theinside of the crucible in a range from 0.6 to 1.0 L, wherein L is adistance extending along the inside surface of the quartz glass cruciblebody, as viewed in cross-section, from the bottom dead center point tothe opening into the quartz glass crucible body and wherein the range of0.15 to 0.55 L is inclusive of the bottom portion and the bent portionand is exclusive of the top portion.
 2. The quartz glass crucible forpulling up a silicon single crystal according to claim 1, characterizedin that an average OH group concentration CA in the transparent layermade of a synthetic quartz glass is from 100 to 300 ppm, an average OHgroup concentration C_(B) in the transparent layer made of naturalquartz glass is from 60 to 150 ppm, an average OH group concentrationC_(C) in the opaque outer layer made of natural quartz glass is from 20to 60 ppm, and they satisfy the relation: CA>C_(B)>C_(C).
 3. A methodfor producing a quartz glass crucible for pulling up a silicon singlecrystal according to claim 1, characterized by making an inner cavity ofa quartz glass crucible base body mounted on a rotatable mold a hightemperature atmosphere, feeding natural silica powder to the hightemperature atmosphere in the inside of an opaque outer layer after orduring the formation of the opaque outer layer by partially melting theinner cavity to form the transparent layer made of natural quartz glasson the entire inner surface of the opaque outer layer by melting andvitrifying the natural silica powder, and then feeding a syntheticsilica powder and melting and vitrifying the synthetic silica powder toform the transparent layer made of a synthetic quartz glass on theinside of the crucible in the range from at least 0.15 to 0.55 L interms of a distance L from the center of the bottom of the inner surfaceof the quartz glass crucible having the transparent layer made ofnatural quartz glass to the upper end face along the inner surface ofthe crucible.
 4. A quartz glass crucible for pulling up a silicon singlecrystal, said quartz glass crucible having an opaque outer layer made ofnatural quartz glass and a transparent layer formed on the insidethereof, characterized in that the number of brown rings per unit area(cm²) observed in the range from the initial surface level of a siliconmelt to 0.3 M in terms of a length M from the initial surface level ofthe silicon melt to the surface level of the remaining melt afterpulling up a single crystal measured along the inner surface of thequartz glass crucible is 1.8-fold or more greater than the number ofbrown rings observed in the range up to 0.3 M above the surface level ofthe remaining melt.
 5. The quartz glass crucible for pulling up asilicon single crystal according to claim 4, characterized in that thenumber of brown rings per unit area (cm²) observed in the range from theinitial surface level of a melt to 0.3 M is 2.5-fold or more greaterthan the number of brown rings observed in the range up to 0.3 M abovethe surface level of the remaining melt.
 6. The quartz glass cruciblefor pulling up a silicon single crystal according to claim 4, saidquartz glass crucible having an opaque outer layer made of naturalquartz glass and a transparent layer formed on the inside thereof,characterized in that a transparent layer made of natural quartz glassor a mixture of natural and synthetic quartz glasses is formed on theinner surface of the crucible in the range from the initial surfacelevel of a silicon melt to 0.3 M in terms of a length M from the initialsurface level of the silicon melt to the surface level of the remainingmelt after pulling up a single crystal measured along the inner surfaceof the quartz glass crucible, a transparent layer made of a syntheticquartz glass is formed on the inner surface of the crucible in the rangeup to 0.3 M above the surface level of the remaining melt, and thenumber of brown rings per unit area (cm²) observed in the range from theinitial surface level of the melt to 0.3 M is 1.8-fold or more greaterthan the number of brown rings observed in the range up to 0.3 M abovethe surface level of the remaining melt.
 7. The quartz glass cruciblefor pulling up a silicon single crystal according to claim 6,characterized in that the number of brown rings per unit area (cm²)observed in the range from the initial surface level of a melt to 0.3 Mis 2.5-fold or more greater than the number of brown rings observed inthe range up to 0.3 M above the surface level of the remaining melt. 8.The quartz glass crucible for pulling up a silicon single crystalaccording to claim 4, said quartz glass crucible having an opaque outerlayer made of natural quartz glass and a transparent layer formed on theinside thereof, characterized in that the inner surface of the cruciblein the range from the initial surface level of a melt to 0.3 M issubjected to an etching treatment or a sandblast process, and the numberof brown rings per unit area (cm²) observed in the range after it isused for pulling up a silicon single crystal is 1.8-fold or more greaterthan the number of brown rings observed in the range up to 0.3 M abovethe surface level of the remaining melt which is not subjected to theetching treatment or the sandblast process.
 9. The quartz glass cruciblefor pulling up a silicon single crystal according to claim 8,characterized in that the number of brown rings per unit area (cm²)observed in the range from the initial surface level of a melt to 0.3 Mis 2.5-fold or more greater than the number of brown rings observed inthe range up to 0.3 M above the surface level of the remaining melt. 10.The quartz glass crucible for pulling up a silicon single crystalaccording to claim 4, characterized in that the number of brown ringsobserved in the range up to 0.3 M above the surface level of theremaining melt is 0.02 to 0.9/cm².
 11. The quartz glass crucible forpulling up a silicon single crystal according to claim 4, characterizedin that the number of brown rings per unit area (cm²) observed in therange from the initial surface level of a melt to 0.3 M is 2.0 to5.0/cm².
 12. A method for producing a quartz glass crucible for pullingup a silicon single crystal according to claim 4, characterized bymaking an inner cavity of a quartz glass crucible base body mounted on arotatable mold a high temperature atmosphere, feeding natural silicapowder or a powder mixture of natural and synthetic silicas to the hightemperature atmosphere in the inside of an opaque outer layer after orduring the formation of the opaque outer layer by partially melting theinner cavity to form a transparent layer made of natural quartz glass ora mixture of natural and synthetic quartz glasses in the range from theinitial surface level of a melt to 0.3 M by melting and vitrifying thenatural silica powder or the powder mixture of natural and syntheticsilicas, and then feeding a synthetic silica powder and melting andvitrifying the synthetic silica powder to form a transparent layer madeof a synthetic quartz glass on the inner surface of the crucible in therange up to 0.3 M above the surface level of the remaining melt.